His heroic role in the revolution and military skill, along with his conciliatory politics toward Shia, Sunnis, Zoroastrians, Jews, and Christians, made him extremely popular among the people. Although it appears that Abu al-'Abbas al-Saffah trusted him in general, he was wary of his power, limiting his entourage to 500 men upon his arrival to Iraq on his way to Hajj in 754. Abu al-'Abbas's brother, al-Mansur (r. 754-775), advised al-Saffah on more than one occasion to have Abu Muslim killed, fearing his rising influence and popularity. It seems that this dislike was mutual, with Abu Muslim aspiring to more power and looking down in disdain on al-Mansur, feeling al-Mansur owed Abu Muslim for his position. When the new caliph's uncle, Abdullah ibn Ali rebelled, Abu Muslim was requested by al-Mansur to crush this rebellion, which he did, and

Abdullah was given to his nephew as a prisoner. Abdullah was ultimately executed.

Relations deteriorated quickly when al-Mansur sent an agent to inventorize the spoils of war, and then appointed Abu Muslim governor of Syria and Egypt, outside his powerbase. After an increasingly acrimonious correspondence between Abu Muslim and al-Mansur, Abu Muslim feared he was going to be killed if he appeared in the presence of the Caliph. He later changed his mind and decided to appear in his presence due to a combination of perceived disobedience, al-Mansur's promise to keep him as governor of Khorasan, and the assurances of some of his close aides, some of whom were bribed by al-Mansur. He went to Iraq to meet al-Mansur in al-Mada'in in 755. Al-Mansur proceeded to enumerate his grievances against Abu Muslim, who kept reminding the Caliph of his efforts to enthrone him. Against Abu Muslim were also charges of being a zindiq or heretic. al-Mansur then signaled five of his guards behind a portico to kill him. Abu Muslim's mutilated body was thrown in the river Tigris, and his commanders were bribed to acquiesce to the murder.

Death

His murder was not well received by the residents of Khorasan, and there was resentment and rebellion among the population over the brutal methods used by Al-Mansur. He became a legendary figure for many in Persia, and several Persian heretics started revolts claiming he had not died and would return; the latter included his own propagandist Ishaq al-Turk, the Zoroastrian cleric Sunpadh in Nishapur, the Abu Muslimiyya subsect of the Kaysanites Shia, and al-Muqanna in Khorasan. Even Babak claimed descent from him